1. Field of the Invention
The present invention relates to vibration-type driving devices. Specifically, it relates to a vibration-type driving device that moves a vibrator and a driven object relative to each other using a combination of vibrations in different vibration modes.
2. Description of the Related Art
For a vibration-type driving device using a vibrator of the type in which vibrations in different vibration modes (shapes) are combined, a configuration in which a plurality of vibrators are provided to ensure the output has been proposed. U.S. Pat. No. 7,466,062 discloses a configuration in which a plurality of vibrators that generate a combination of vibrations in a longitudinal vibration mode in the longitudinal direction of the vibrator and an out-of-plane bending vibration mode are disposed on concentric circles and in which a driven object that is to come into pressure contact with the plurality of vibrators is rotated relative to the plurality of vibrators.
One problem with the vibration-type driving device using a vibrator of the type in which vibrations in different vibration modes are combined has a plurality of vibrators to ensure the output is a decrease in operating life. The operating life of the vibration-type driving device sometimes depends on the wear of contact regions (sliding regions) of the driven object with which contact portions of the vibrators are to come into contact.
In the vibration-type driving device disclosed in U.S. Pat. No. 7,466,062, the rotation angle of the driven object is not particularly limited, and the driven object rotates at a desired rotation angle. Furthermore, in the case of the foregoing vibration-type driving device, the contact regions of the driven object are the same for the plurality of vibrators. Therefore, the amount of wear at the contact regions of the driven object increases substantially in proportion to an increase in the number of vibrators, as compared with a case in which one vibrator is used. This may promote the decrease of the life of the vibration-type driving device. Furthermore, for the case where only the amount of wear of a portion of the contact regions is larger than that at the other portions, the life may expire because the amount of wear of the portion reaches the limit even if the other portions maintain the performance.
FIGS. 14A and 14B schematically show the state of local wear described above. This will be described using an example in which contact portions of two vibrators (not shown) are in pressure contact with one surface of a driven object 5. FIG. 14A shows contact regions A1 and A2 of the driven object 5 relative to two vibrators in a hatch pattern. The contact regions A1 and A2 overlap substantially in the center of the driven object 5. FIG. 14B shows the schematic cross-sectional view of the wear of the driven object 5 caused by the operation of the vibration-type driving device. A cross section only at the contact region A1 is denoted by C1, a cross section only at the contact region A2 is denoted by C2, and a cross section at which the contact regions A1 and A2 overlap is denoted by C3. Sections C1 and C2 individually come into friction contact with one vibrator, while section C3 comes into friction contact with two vibrators. Therefore, section C3 is worn substantially twice as much as sections C1 and C2. When section C3 is worn to the limit, the life of the vibration-type driving device expires.